Every year I shoot a doe or two during the summer under an agricultural damage permit. The farm I hunt is about 1 1/2 hours away. After registration, I buy 3 bags of ice. I put two inside the body cavity end to end and lay one across the shoulders in the back of my capped pickup on the way home.
When I get home, the deer goes onto the garage floor with the ice that's left and a couple of ice jugs from the freezer. She gets covered by a tarp and a couple of old blankets overnight.
She gets cut up right away the next morning. Typical temperatures in July/August are in the 80's during the day. I've treated the deer in this manner for several years and have not had one go bad yet.